Vehicle weight measurements are useful in a wide variety of applications including rail transport, heavy mining and farm operations. The weight of a salt spreader or manure truck monitored in real time helps control application rates, for example. The weight history of a grain cart or sugar cane cart is directly related to crop yield measurements. A sugar cane harvesting company, as an example, may have as many as ten harvest teams working at once. Each team may include ten trains of three cane carts that move cane from the fields to the mill where sugar is extracted. The weight of each one of the 300 carts represents valuable information for yield monitoring, load integrity, shipping cost accounting, and mill workload prediction among other uses.
Vehicles may be weighed at fixed weigh bridges or on portable weigh pads, but these measurements are available only at the location of the weighing equipment. Vehicles may also be equipped with load cells installed in the vehicle underbody or on wheel hubs. Load cells are expensive (roughly $3,000 or more per vehicle), however, and their design varies for different types of vehicles. Installing load cells often involves temporarily removing vehicle wheels, and welding fixtures into place.
Vehicles that have suspensions may weigh themselves by monitoring deflection of suspension components such as springs. However, many farm and other vehicles do not have suspensions. Tire deformation or deflection measurements are also indicative of weight on wheels, but tire measurements are affected by tire pressure, which is not always well controlled, and ground stiffness, which is highly variable in an off-road environment.
Therefore, what are needed are systems and methods for weighing vehicles. These systems should work while the vehicles are in motion or stationary. They should work on vehicles that lack suspensions and that travel slowly over soft, uneven ground. Finally, they should be inexpensive and easy to install.